The present invention relates to an endoscope apparatus using a solid-state image pickup device which is inserted in a body cavity to pick up an image thereof.
A typical conventional endoscope apparatus uses a fiberscope having an image guide with a bundle of optical fibers.
An improved conventional endoscope has been proposed along with the development of a very compact solid-state image pickup device in recent years. In such an endoscope, the solid-state image pickup device is mounted in the distal end of an insertion portion of the endoscope, and an image of an object to be examined is directly picked up and extracted as a video signal without using an image guide fiber. The extracted video signal is displayed as an image on a TV monitor. Medical diagnosis according to this apparatus is performed through the TV monitor.
In the solid-state image pickup device, signal charges stored in light-receiving portions upon reception of light therein are transferred to vertical transfer portions from the light-receiving portions during the blanking period. When this transfer is completed, new signal charges are started. The transferred charges are sequentially transferred to a horizontal transfer portion according to a TV (scanning) system and then extracted outside the solid-state image pickup device. Illumination of a photographing portion in the body cavity may be performed regardless of the type of light, i.e., continuous light or light pulses.
Diagnosis and therapy using an endoscope are performed such that a doctor observes an image on a realtime basis. An image may be photographed to perform an objective diagnosis and to check an effect of the treatment.
In a conventional endoscope using a fiberscope, a camera is attached to the eyepiece of the probe to take a picture of the object to be examined. In this case, an exposure time can be arbitrarily determined by a shutter speed of the still camera to obtain an image without blurring in a short exposure period. Underexposure is compensated by a flash light source or the like, and thus an exposure time can be further shortened.
In a conventional endoscope apparatus using a solid-state image pickup device, since an image on a TV monitor is photographed, the display image must be frozen (the display image is temporarily processed to obtain a still image). More specifically, a frame memory is arranged in a video processor for processing an image signal. One-frame image data is stored in the frame memory, and the stored image data is repeatedly read out and displayed to obtain a still image. According to a standard interlaced scanning system such as an NTSC (National Television System Committee), a period required for forming a one-field image is 1/60 sec, and a period required for forming a one-frame image is 1/30 sec corresponding to the two-field time. If an image to be stored in the frame memory is a one-frame image, a time lag of about 1/30 sec occurs. Even if a one-field image is written in the frame memory, a time lag of 1/60 sec occurs. In particular, if a dynamic body portion such as an esophagus subjected to an influence of heart beats is to be photographed, blurring typically occurs. Such blurring degrades not only the quality of the still image but also of the moving image.
In order to observe a body cavity with an endoscope, the intensity of illumination light must be controlled according to brightness of an object to be examined, e.g., a body cavity wall. In a conventional endoscope apparatus using an image guide fiber, the brightness of the object is measured through the image guide fiber, and control is provided to set the measured value within a predetermined range.
A portion as an object to be examined with an endoscope is a spatially narrow portion. However, in such a narrow portion, portions to be examined have significantly different distances from the distal end of the insertion portion of the endoscope and have different brightness levels.